This study proposes to investigate the factors that influence the regeneration of skeletal muscle fiber types. Two factors are important to this study. 1) Free grafting of skeletal muscle results in the regeneration of a muscle containing muscle spindles, while regeneration induced by mincing or slicing will produce no muscle spindles; 2) different muscles can be selected for their homogeneity of fiber types or the distinct patterns of their fiber type distribution. Therefore, by comparing transplanted freely-grafted muscles to minced or sliced muscles, the regenerated muscle will show the influence of muscle spindles on the patterns of fiber types regenerated. Furthermore, by transplantation of muscles of one fiber type into a site containing a different fiber type and observing the type of muscle regenerated, we can determine the relative influence of the donor muscle type versus the host innervation pattern in establishing the regenerated muscle. Finally, we wish to determine whether a muscle can be surgically enlarged in both structure and function by using strips of grafted muscles. We wish to determine the factors that influence the success of this procedure. The muscles will be analyzed by using electron microscopy, histochemistry and physiology. Avian muscles will be used for these studies because these muscles can be selected for the homogeneity of muscle fiber types or patterns of fiber type distribution. This will ensure less chance for misinterpretation of results. These studies have potential value in the clinical treatment of myopathies and are important to the understanding of neuromuscular interactions, and the development and maintenance of the differentiated skeletal muscle.